The present invention relates to an improvement of an elevator apparatus and, more particularly, to an improved elevator apparatus having an enhanced level of safety at the time when the brake device is out of normal operation.
In general, an elevator driving system is of a type wherein sheaves are rotated by an electric motor and an elevator cage and a balance weight suspended from the sheaves in the form of a well bucket are raised or lowered. In many cases, therefore, the sheaves are affected by an unbalance torque due to the difference in weight between the elevator cage and the balance weight. Therefore, a brake device, which functions to stop and retain or support the elevator cage at their stopped position, is required to have a high level of safety.
For the above-mentioned reasons, a rigid drum type electromagnetic brake, which is disclosed in, for example, Japanese Patent Unexamined Publication No. 57-1180, has hitherto been employed.
Meanwhile, in an elevator equipped with a gear reducer called "geared elevator", a worm gear reducer has hitherto been employed. With this worm gear, the efficiency of torque transmission from an electric motor to sheaves is very high whereas the retrograde efficiency of torque transmission from the sheaves to an electric motor is considerably low. Accordingly, this worm gear reducer is advantageous in respect of lessening the possibility that the normal rotation of the electric motor is hindered by the unbalance torque.
On the other hand, the use of a parallel axis gear reducer has recently been proposed in place of such worm gear reducer.
In this case, however, the retrograde efficiency also is increased with the result that much more care must be taken about the safety of the brake device.
Further, for miniaturization of the brake device, change-over from the drum type electromagnetic brake device to a disk type brake device has also been proposed.
In the field of a disk type brake device, detection of the operating condition of a brake device is known as disclosed in Japanese Patent Unexamined Publication No. 58-109741.
Further, in the field of an elevator, it is known that an unbalance torque is detected on the basis of an amount of displacement of a retainer or support section for the electromagnetic brake device to thereby be used for control of the brake as in said Japanese Patent Unexamined Publication No. 57-1180, or that an unbalance torque as in Japanese Patent Unexamined Publication No. 62-56277 is detected on the basis of distortion of a retainer section for the electromagnetic brake device to thereby be used for control of, for example, starting compensation for an elevator.
The safety and reliability of brake devices including the disk type brake device, etc. have already been established. In case of elevators, however, it is desirable to take perfect measures for safety.
What is the most important matter for the brake device of an elevator is as follows. Namely, during the running of an elevator, electricity is supplied to braking coils. When, however, the attractive force of the braking coils has decreased for some malfunction to amount to half of a normal attractive force, an armature of the brake is caused to contact with a lining thereof while the latter is being rotated. The wear of the lining thus is further vigorous due to the friction between the two until a braking force could not be obtained even if the supply of electricity to the coils is paused. This is a very important point which may lead to accidents resulting in injury or death, for the brake device for causing the elevator to be stopped and supported or retained at its stopped position.
In an elevator including many operating conditions, or in an elevator in which an unbalance torque always acts, it is desirable to prevent the occurrence of any accident when some malfunction occurs in the brake device including a disk brake device and the like. To this end, it is also desirable to realize such a system as would be able to prevent the occurrence of any such accident.